An outburst of deadly violence in neighbouring Ukraine is casting a pall over the final days of the Winter Olympics.

Host Russia began the Games with a call for a worldwide truce during the Olympic period, but by Wednesday it was trading blame with the United States and European Union over the bloodshed in Ukraine, which killed at least 25 people on Tuesday and Wednesday. Russia has steadfastly backed Ukrainian President Viktor Yanukovych throughout the three-month-old crisis, while the U.S. and EU have encouraged the opposition that is now battling police in the streets of Kiev.

"Those are terrible scenes," Mark Adams, a spokesman for the International Olympic Committee, said, referring to the television images of the fiery streetfights. "The Olympic truce is an important, symbolic thing for us – I'm not sure really that it plays much part in what's going on there but clearly we hope that the situation will be solved as quickly and with as less bloodshed as possible."

The Ukrainian Olympic Committee said its athletes had asked for permission to wear black armbands in competition, as a gesture of mourning for those killed in Kiev. However, the Ukrainian team said the IOC rejected the request, citing the Olympic Charter's ban on any kind of political or religious statements on athletes' clothing.

The fighting began Tuesday after Ukraine's parliament refused to table an opposition effort to alter the country's constitution to curb Mr. Yanukovych's powers. But the struggle for Ukraine dates back to Nov. 21, when Mr. Yanukovych – under heavy Russian pressure – shocked his country by walking away from an EU trade deal in favour of closer ties with Moscow.

The stakes are high for all sides. Russia's Foreign Ministry issued a belligerent statement Wednesday accusing "radical opposition leaders" of trying to violently seize power in Ukraine. "We do not see a coherent response from European politicians and institutions, which refuse to recognize that the responsibility for the actions of the radical forces in Ukraine lies on the opposition."

The statement demanded that "leaders of the (opposition) stop the bloodshed," adding "Ukraine is a friendly brother state and a strategic partner, and we will use all our influence in order for peace and calm to reign." The statement, posted on the Foreign Ministry's website, did not specify what measures Moscow might take.

Meanwhile, France and Poland called for targeted sanctions against the Ukrainian leadership, and an emergency meeting of EU foreign ministers will be held Thursday.

The new violence broke out just hours after the Kremlin announced it was freeing up $2-billion in financial aid to Ukraine that it had frozen after Mr. Yanukovych made a series of concessions to the opposition.

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Russian President Vladimir Putin's press secretary told Russian media that Mr. Putin and Mr. Yanukovych spoke by telephone during the violence Tuesday night. But spokesman Dmitry Peskov denied that Mr. Putin was influencing decisions in Ukraine. "Russia's president never has and does not give advice to his Ukrainian colleague about what to do."

Sergey Bubka, the pole-vaulting legend who heads Ukraine's 43-athlete team in Sochi, pleaded via his Twitter account for a halt to the violence.

"I want to bring Olympic truce to my country. Dialogue is power, violence is weakness," wrote Mr. Bubka, a former parliamentary deputy in Mr. Yanukovych's Party of Regions. "Our athletes are competing hard in Sochi, but peacefully and with honour. Violence has no place in the World."

Ukraine has won one medal so far in Sochi, a bronze in women's biathlon achieved by Vita Seremenko.

"Yes it's a distraction, everyone's talking about it – even just now at the start, at the finish, people are saying 'what's happened in your country, what's happened?'" said Kiev native Dmytro Mytsak, after finishing 67th in Wednesday's giant slalom final.

In Olympic Village restaurants, footage of the violence in Kiev – which is portrayed in Russian media as a police operation against armed radicals – was shown on one television set, while the next showed highlights of Russia's hockey win over Norway on Tuesday night.

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The violence was doing the Ukrainian city of Lviv no favours as it bids to host the 2022 Winter Games. Lviv, which is in the opposition stronghold of Western Ukraine, was largely in the hands of protesters Wednesday, who had seized the main government buildings and police stations.

Mr. Adams of the IOC said it was premature to speculate on what effect the violence might have on Lviv's Olympic bid. The other cities in the running for the 2022 Games are Beijing, Oslo, the Polish city of Krakow and Almaty, in Kazakhstan. A decision will be made at an IOC meeting next year.